Tissue structure and strength are the most relevant properties when assessing animal models related to musculoskeletal injury, disease and repair. Whether the treatment effects are created by genetic manipulation, metabolic challenge, simulated injury, surgical repair or other intervention, the net effects must be judged based on whether they have resulted in more or less tissue, whether that tissue has normal morphology, and whether the tissue or skeletal structure has increased or decreased mechanical properties. We have the necessary equipment and the demonstrated user expertise to assess the structural and mechanical properties of a range of musculoskeletal tissue and structures derived from animal models. There have been productive collaborations between investigators in the Research Base and the personnel of this Core, but these have been limited in number by the lack of a mechanism to support the acquisition and analysis of data by expert users and the training of non-expert users. The objective of this Musculoskeletal Structure and Strength Core (Core B) is to provide a mechanism to increase access to existing resources for x-ray based densitometry and imaging, and mechanical testing, and to thereby enable new interactions and enhance existing interactions between musculoskeletal researchers at Washington University. We will maintain protocols and equipment to promote quality control, provide technical support and training, and perform the following services on musculoskeletal structures and tissues from animal models (mouse to canine) generated by investigators in the Core Center Research Base. Aim 1: X-ray based imaging; available modalities include radiography, dual-energy x-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT) and micro-computed tomography (microCT). Each of these is available for ex vivo or in vivo imaging. Aim 2: Mechanical testing;available modalities include whole-bone bending and compression, trabecular indentation, tensile testing of demineralized bone, tendon and tendon-bone insertion site tensile testing;muscle force measurement. By offering these Core services we will increase research productivity of established musculoskeletal investigators on our campus and facilitate non-musculoskeletal investigators wishing to bring new perspectives to studies in musculoskeletal biology and medicine.